Abstract 419: Two Models of Endothelial Dysfunction: the Importance of Intrinsic Cardioprotective Properties of the Coronary-endothelium

Abstract

The coronary endothelium plays a major role in protecting cardiomyocytes (CMs) from hypoxia/reoxygenation injury. We are describing two models of endothelial dysfunction compromising the intrinsic cardioprotective properties of endothelial cells (ECs). Tetrahydrobiopterin (BH4) is an essential cofactor for coupling of endothelial nitric oxide synthase (eNOS) to produce the cardioprotective mediator nitric oxide (NO). However, hyperglycemia (HG) leads to significant increases in oxidative stress, oxidizing BH4 to dihydrobiopterin and thereby causing endothelial dysfunction. Additionally, Langendorff-perfused mouse hearts were treated by triton X-100 to produce endothelial dysfunction and subsequently subjected to 30 min of ischemia followed by 2 h of reperfusion. The recovery of left ventricular systolic and diastolic function during reperfusion was impaired in triton X-100 treated hearts compared with vehicle-treated hearts. CMs were co-cultured with ECs and subsequently subjected to 2 h of hypoxia followed by 2 h of reoxygenation. Addition of ECs to CMs at a ratio of 1:3 significantly increased NO production and decreased lactate dehydrogenase activity compared with CMs alone. This EC-derived protection was abolished by HG. The addition of 100 μM sepiapterin (a BH4 precursor) or overexpression of GTP cyclohydrolase 1 (the rate-limiting enzyme for BH4 biosynthesis) in ECs by gene trasfer enhanced endothelial BH4 levels, the ratio of eNOS dimer/monomer, eNOS phosphorylation, and NO production and decreased lactate dehydrogenase activity in the presence of HG. These results demonstrate the important intrinsic cardioprotective properties of the coronary endothelium, more specifically increased BH4 content in ECs by either pharmacological or genetic approaches reduces myocardial damage during hypoxia/reoxygenation in the presence of HG. Maintaining sufficient endothelial BH4 is crucial for cardioprotection against hypoxia/reoxygenation injury.